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MC và các hệ thống phổ Bá P2

MC-CDMA and MC-DS-CDMA In this chapter, the different concepts of the combination of multi-carrier transmission with spread spectrum, namely MC-CDMA and MC-DS-CDMA are analyzed. Several single-user and multiuser detection strategies and their performance in terms of BER and spectral efficiency in a mobile communications system are examined. 2.1 MC-CDMA 2.1.1 Signal Structure The basic MC-CDMA signal is generated by a serial concatenation of classical DSCDMA and OFDM. Each chip of the direct sequence spread data symbol is mapped onto a different sub-carrier. Thus, with MC-CDMA the chips of a spread data symbol are transmitted in parallel on different sub-carriers, in contrast to a. | 2 MC-CDMA and MC-DS-CDMA In this chapter the different concepts of the combination of multi-carrier transmission with spread spectrum namely MC-CDMA and MC-DS-CDMA are analyzed. Several single-user and multiuser detection strategies and their performance in terms of BER and spectral efficiency in a mobile communications system are examined. 2.1 MC-CDMA 2.1.1 Signal Structure The basic MC-CDMA signal is generated by a serial concatenation of classical DS-CDMA and OFDM. Each chip of the direct sequence spread data symbol is mapped onto a different sub-carrier. Thus with MC-CDMA the chips of a spread data symbol are transmitted in parallel on different sub-carriers in contrast to a serial transmission with DS-CDMA. The number of simultaneously active users1 in an MC-CDMA mobile radio system is K. Figure 2-1 shows multi-carrier spectrum spreading of one complex-valued data symbol d k assigned to user k. The rate of the serial data symbols is 1 Td. For brevity but without loss of generality the MC-CDMA signal generation is described for a single data symbol per user as far as possible such that the data symbol index can be omitted. In the transmitter the complex-valued data symbol d k is multiplied with the user specific spreading code c k _ c k ck ck T 2 1 c c0 c1 cL 1 Z .i of length L PG. The chip rate of the serial spreading code c k before serial-to-parallel conversion is 1L 2.2 Tc J-d 1 Values and functions related to user k are marked by the index k where k may take on the values 0 . K - 1. Multi-Carrier and Spread Spectrum Systems K. Fazel and S. Kaiser 2003 John Wiley Sons Ltd ISBN 0-470-84899-5 50 MC-CDMA and MC-DS-CDMA Figure 2-1 Multi-carrier spread spectrum signal generation and it is L times higher than the data symbol rate 1 Td. The complex-valued sequence obtained after spreading is given in vector notations by s k d k c k S k S k S k T 2 3 s C kJ0 1 . . . L1 .D A multi-carrier spread spectrum signal is obtained after modulating the components S k l 0 . L